Method for avoiding die cracking

ABSTRACT

Methods directed to avoiding die cracking resulting from die separation are described herein. A method may include providing a substrate including a first die, a second die, and a monitor structure in an area between the first die and the second die, the monitor structure including a first dielectric material, removing the first dielectric material from the monitor structure, and after removing the first dielectric material, cutting the substrate along the area between the first die and the second die to separate the first die from the second die.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 60/991,057, filed Nov. 29, 2007, the entire disclosureof which is hereby incorporated by reference in its entirety for allpurposes except for those sections, if any, that are inconsistent withthis specification.

TECHNICAL FIELD

Embodiments of the present invention relate to the field ofmicroelectronics, in particular, to methods for avoiding die crackingresulting from die separation.

BACKGROUND

Integrated circuits are typically formed on a wafer, which is then cutto singulate the individual dies. Singulating the dies may sometimesresult in cracks that propagate from the dicing saw throughout the waferand into the integrated circuit. For semiconductor devices includinglow-k (low-dielectric constant) interlayer dielectrics, the crackingproblem may be even more problematic due at least in part to the pooradhesion and fragility of low-K dielectrics.

Some have attempted to mitigate cracking by laser-grooving the sawstreets prior to sawing. Laser-grooving is accompanied by its ownproblems including the time-consuming aspect of laser-grooving thestreets one at a time. As dies become even smaller, the time required tolaser-groove all streets increases. Furthermore, laser-grooving is knownto result in contamination of the dies from the settling of materialvaporized by the laser. This contamination may result in degradation ofthe reliability of the dies.

SUMMARY

In view of the problems in the state of the art, embodiments of theinvention are directed to methods for avoiding die cracking resultingfrom die separation. More specifically, with the foregoing and otheritems in view, there is provided, in accordance with various embodimentsof the invention, a method comprising providing a substrate including afirst die, a second die, and a monitor structure in an area between thefirst die and the second die, the monitor structure including a firstdielectric material. The method further comprises removing the firstdielectric material from the monitor structure, and after removing thefirst dielectric material, cutting the substrate along the area betweenthe first die and the second die to separate the first die from thesecond die.

In some embodiments, the substrate may include a second dielectricmaterial between the monitor structure and the first die, and betweenthe monitor structure and the second die. The first dielectric materialand the second dielectric material may comprise the same material. Invarious embodiments, the method may further comprise removing the seconddielectric material. The second dielectric material may be removed byanisotropic etching.

In some embodiments, the monitor structure may be a process controlmonitor structure.

In some embodiments, the providing of the substrate may comprise formingthe first die, the second die, and the monitor structure on thesubstrate.

In some embodiments, the first dielectric material may be a low-kdielectric oxide.

In some embodiments, the method may further comprise forming aphotoresist layer over the first die, the second die, and the monitorstructure, and patterning the photoresist layer to reveal the monitorstructure. In some embodiments, the removing of the first dielectricmaterial may comprise removing the first dielectric material from therevealed monitor structure. In some embodiments, the method may compriseremoving the photoresist layer after removing the first dielectricmaterial from the revealed monitor structure.

In some embodiments, the first dielectric material may be removed byisotropic etching.

In some embodiments, the method may comprise removing the monitorstructure. In some embodiments, the cutting of the substrate may beperformed after removing the monitor structure.

In some embodiments, the dielectric material may be disposed in aplurality of saw streets.

Other features that are considered as characteristic for embodiments ofthe invention are set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be readily understood by thefollowing detailed description in conjunction with the accompanyingdrawings. To facilitate this description, like reference numeralsdesignate like structural elements. Embodiments of the invention areillustrated by way of example and not by way of limitation in thefigures of the accompanying drawings.

FIG. 1 illustrates a cross-sectional view of substrate including diesseparated a dielectric material and a monitor structure in accordancewith various embodiments of the present invention.

FIGS. 2-12 illustrate cross-sectional views of the substrate of FIG. 1at various stages of a method in accordance with various embodiments ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration embodiments in which the invention may be practiced. It isto be understood that other embodiments may be utilized and structuralor logical changes may be made without departing from the scope of thepresent invention. Therefore, the following detailed description is notto be taken in a limiting sense, and the scope of embodiments inaccordance with the present invention is defined by the appended claimsand their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments ofthe present invention; however, the order of description should not beconstrued to imply that these operations are order dependent. Moreover,some embodiments may include more or fewer operations than may bedescribed.

The description may use the phrases “in an embodiment,” “inembodiments,” or “in various embodiments,” which may each refer to oneor more of the same or different embodiments. Furthermore, the terms“comprising,” “including,” “having,” and the like, as used with respectto embodiments of the present invention, are synonymous.

For purposes of this description, the phrase “A/B” means A or B. Thephrase “A and/or B” means “(A), (B), or (A and B).” The phrase “at leastone of A, B, and C” means “(A), (B), (C), (A and B), (A and C), (B andC), or (A, B, and C).” The phrase “(A)B” means “(B) or (AB),” that is, Ais an optional element.

The terms chip, die, integrated circuit, monolithic device,semiconductor device, and microelectronic device are often usedinterchangeably in the microelectronics field. The present invention isapplicable to all of the above as they are generally understood in thefield.

Various embodiments of the present invention are directed to avoidingdie cracking resulting from die separation. In various embodiments, diecracking may be avoided by removing material between dies before cuttingthe dies apart. By removing the material between the dies first, theedges of the dies may experience a reduced level of stress, relative tovarious related methods allowing such material to remain. This reducedlevel of stress may result in elimination of cracking of the die duringseparation. In some embodiments, the material between the dies may beremoved by an etch operation, which may be faster and less likely tocontaminate the dies.

Turning now to FIG. 1, an apparatus comprising a substrate 100 includinga plurality of dies 102 separated from each other by at least a materialsuch as, for example, a dielectric material 104. The substrate 100 maycomprise any substrate suitable for forming the plurality of dies 102thereon. In some embodiments, for example, the substrate 100 may besilicon, silicon carbide, sapphire, gallium arsenide (or other III-IVmaterial). In some embodiments, the dies 102 may be formed from one ormore epitaxial layers formed on the substrate 100.

The dielectric material 104 may be any material generally disposedbetween dies for separating the active regions of the dies 102. In fact,in some embodiments, the material used to separate the dies may be anon-dielectric material. For embodiments in which a dielectric materialis used, the dielectric material 104 may be one or more of an oxide, anitride, and the like. In some embodiments, the oxide may be a low-kdielectric material. The dielectric material 104 may comprise one layeror may comprise a plurality of layers of the same or different material.For example, the dielectric material 104 may comprise a layer of oxideon a layer of nitride, or vice versa.

The substrate 100 may include at least one monitor structure 106. Asillustrated, the monitor structure 106 may be disposed between at leasttwo of the dies 102, further separating the dies 102 in addition to thedielectric material 104. In some embodiments, the dielectric material104 may be disposed between the monitor structure 106 and the dies 102,as illustrated.

The monitor structure 106 may be any feature formed on the substrate 100during processing for various purposes including, for example, aiding incharacterizing or identifying defects in a process or design. Themonitor structure 106 may be, for example, a process control monitorstructure for yielding information predictive of the performance of acircuit with respect to its design specifications. Such data may becollected and analyzed to determine, for example, whether a die is“good” or “bad.” In some embodiments, the monitor structure 106 may beidentical to one or more of the dies 102, or may be some structureindicative of a process or design (e.g., structures to monitor defectdensity, dielectric coverage, sheet resistance, leakage, etc.).

The monitor structure 106 may be formed, at least in part, with adielectric material. The dielectric material may be the same as thedielectric material 104, or it may be a different material. Thedielectric material 104 may be one or more of an oxide, a nitride, andthe like. In some embodiments, the oxide may be a low-k dielectricmaterial.

Conventionally, the structure of FIG. 1 may undergo a cutting operationto singulate the dies 102. For such an operation, the structure may becut generally along a saw street 108. As illustrated, the saw street 108may generally include the monitor structure and at least some of thedielectric material 104. Cutting along the saw street 108 may, however,cause cracking in one or more of the dies 102 and/or the substrate 100.This cracking may result from the sheer force along the junction of themetal of the dies 102 and the dielectric material 104.

To avoid cracking, the dielectric material 104 and the monitor structure106 may be removed prior to singulating the dies 102. FIGS. 2-12illustrate an exemplary method for avoiding cracking of the apparatusillustrated in FIG. 1 by way of cross-sectional side views of theapparatus at various stages of the method. It should be noted thatvarious operations discussed and/or illustrated may be generallyreferred to as multiple discrete operations in turn to help inunderstanding embodiments of the present invention. The order ofdescription should not be construed to imply that these operations areorder dependent, unless explicitly stated. Moreover, some embodimentsmay include more or fewer operations than may be described.

To selectively remove the dielectric material 104, while leaving otherareas undamaged, a photolithographic operation may be used for exposingonly those areas that include material to be removed. As illustrated inFIG. 2, such a method may include forming a photoresist layer 110 overat least the dies 102. As photoresist is typically applied byspin-coating, it may be the case that the photoresist layer 110 isapplied over the entire surface including over the dielectric material104 and the monitor structure 106.

The photoresist layer 110 may then be patterned as illustrated in FIGS.3 and 4. Patterning may include exposing the desired pattern ofradiation 112 onto the surface of the photoresist layer 110 using a mask114. In the illustrated embodiment, the exposed pattern corresponds tothe locations of the dielectric material 104 to be removed. Although theillustrated embodiment depicts the photoresist layer 110 as being apositive photoresist, a negative photoresist may be similarly suitable.

Patterning the photoresist layer 110 may further include developing thepattern as illustrated in FIG. 4. The exposed regions of the photoresistlayer 110 (or un-exposed regions if a negative photoresist is used) areremoved to reveal the dielectric material 104 thereunder. The exposedregions of the photoresist layer 110 may be removed by any methodsuitable for the purpose including, for example, a rinse operation.

The revealed dielectric material 104 may be removed as illustrated inFIG. 5. The revealed dielectric material 104 may be removed using anyetch operation suitable for the purpose. In some embodiments, forexample, the revealed dielectric material may be removed using ananisotropic etch (e.g., a dry etch). It may be possible, however, to usean isotropic etch.

Next, the dielectric material 104 may be removed, leaving gaps 116, asillustrated in FIG. 5. In the illustrated embodiment, gaps 116 areformed between the monitor structure 106 and the dies 102. Inembodiments not including the monitor structure 106, the gaps may bebetween adjacent dies 102. Although the illustrated embodiment depictsthe dielectric material 104 being completely removed, a beneficialreduction in cracking may be achieved by removing even less than all ofthe dielectric material 104. In many embodiments, however, thedielectric material 104 will be removed substantially down to thesubstrate 102, although some dielectric material 104 may remain inlocations as desired (e.g., on the sidewalls of the dies 102).

Next, the photoresist layer 110 may be removed as illustrated in FIG. 6using any suitable photoresist strip operation.

As illustrated in FIG. 7, another photoresist layer 118 may be formedover at least the dies 102. As photoresist is typically applied byspin-coating, it may be the case that the photoresist layer 110 isapplied over the entire surface including over the dielectric material104 and the monitor structure 106.

The photoresist layer 118 may then be patterned by exposing the desiredpattern of radiation 120 onto the surface of the photoresist layer 118using a mask 122. In the illustrated embodiment, the exposed patterncorresponds generally to the location of the monitor structure 106.Although the illustrated embodiment depicts the photoresist layer 118 asbeing a positive photoresist, a negative photoresist may be similarlysuitable.

Patterning the photoresist layer 118 may further include developing thepattern as illustrated in FIG. 8. The exposed regions of the photoresistlayer 118 (or un-exposed regions if a negative photoresist is used) areremoved to reveal the monitor structure 106 thereunder. The exposedregions of the photoresist layer 118 may be removed by any methodsuitable for the purpose including, for example, a rinse operation.

Dielectric material in the revealed monitor structure 106 may beremoved. The dielectric material of the revealed monitor structure 106may be removed using any etch operation suitable for purpose. In someembodiments, for example, the dielectric material may be removed usingan isotropic etch (e.g., a wet etch) as illustrated in FIG. 9. Theisotropic etch etches in a multi-directional manner and thus the etchingaction 124 may be capable of attacking all exposed surfaces of themonitor structure 106.

As the monitor structure 106 may comprise material in addition todielectric material (e.g., metal), a collapsed structure of material 126may remain after removing the dielectric material from the monitorstructure 106 as illustrated in FIG. 10. In some embodiments, however,the remaining material 126 may be washed away by the etch operation (seeFIG. 9). This may especially be the case if the dielectric materialadhering the monitor structure 106 to the substrate 100 is etched away.

If material 126 remains after the etch operation, a rinse operation maybe used for clearing away such material, if desired, as illustrated inFIG. 11. In some embodiments, the remaining material 126 need not beremoved. The photoresist layer 118 may also be removed as illustrated inFIG. 11 using any suitable photoresist strip operation. In someembodiments, the photoresist strip operation may be sufficient to removethe remaining material 126.

The dies 102 may then be singulated by cutting the substrate 100 alongthe saw street 108, resulting in the singulated dies 102 as illustratedin FIG. 12. Singulating the dies 102 may be accomplished using anymethod suitable for the purpose including, for example, sawing.

As discussed herein, owing at least in part to the removal of thedielectric material 104 and the monitor structure 106, the dies 102 mayhave less cracking relative to methods allowing the dielectric material104 and/or monitor structure 106 to remain in place. Moreover, thedielectric material 104 between the dies 102 may be removed faster andwith less contamination relative to laser-grooving methods.

Although certain embodiments have been illustrated and described hereinfor purposes of description of a preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent embodiments or implementations calculated toachieve the same purposes may be substituted for the embodimentsillustrated and described without departing from the scope of thepresent invention. Those with skill in the art will readily appreciatethat embodiments in accordance with the present invention may beimplemented in a very wide variety of ways. This application is intendedto cover any adaptations or variations of the embodiments discussedherein. Therefore, it is manifestly intended that embodiments inaccordance with the present invention be limited only by the claims andthe equivalents thereof.

1. A method comprising: providing a substrate including a first die, asecond die, and a monitor structure, the substrate further including afirst dielectric material between the monitor structure and the firstdie and between the monitor structure and the second die, and themonitor structure including a second dielectric material; forming afirst photoresist layer over the first die, the second die, the monitorstructure, and the first dielectric material; patterning the firstphotoresist layer to reveal the first dielectric material between themonitor structure and the first die, and between the monitor structureand the second die; etching the first dielectric material between themonitor structure and the first die, and between the monitor structureand the second die; removing the first photoresist layer after etchingthe first dielectric material; forming a second photoresist layer overthe first die, the second die, the monitor structure, and the firstdielectric material; patterning the second photoresist layer to revealthe monitor structure; etching the second dielectric material from themonitor structure; and cutting the substrate between the first die andthe second die to separate the first die from the second die.
 2. Themethod of claim 1, wherein the monitor structure is a process controlmonitor structure.
 3. The method of claim 1, wherein the providing ofthe substrate comprises forming the first die, the second die, themonitor structure, and the first dielectric material.
 4. The method ofclaim 1, wherein the first and the second dielectric material comprise alow-k dielectric oxide.
 5. The method of claim 1, wherein the etching ofthe first dielectric material between the monitor structure and thefirst die, and between the monitor structure and the second diecomprises dry etching the revealed first dielectric material.
 6. Themethod of claim 1, wherein the etching of the second dielectric materialfrom the monitor structure comprises wet etching the revealed monitorstructure.
 7. The method of claim 1, further comprising removing thesecond photoresist layer after etching the revealed monitor structure.8. The method of claim 1, further comprising removing the monitorstructure having the second dielectric material removed therefrom, andwherein the cutting of the substrate is performed after removing themonitor structure.
 9. The method of claim 1, wherein the monitorstructure and the first dielectric material are disposed in a pluralityof saw streets.
 10. The method of claim 1, wherein the first dielectricmaterial between the monitor structure and the first die, and betweenthe monitor structure and the second die, is anisotropically etched, andwherein the second dielectric material is isotropically etched from themonitor structure.